The present invention relates to a capping unit for an ink jet recording head incorporated in an ink jet recording apparatus, and a method of manufacturing the same. In particular, the ink jet recording apparatus comprises: an ink jet recording head installed on a carriage moved in the widthwise direction of recording paper, for jetting ink droplets from nozzle orifices by pressurizing ink from an ink tank supplied into associated pressure generating chamber by a pressure generating member such as piezoelectric vibrators, heating elements or the like; and a capping unit provided with a capping member for sealing a surface of the recording head on which the nozzle orifices are formed (hereinafter, the nozzle-formed surface), and receiving negative pressure generated by a negative pressure generating member, wherein vaporization of an ink solvent from the capping member is inhibited during the halt of recording operation in order to prevent from clogging of the nozzle orifices.
As for an ink jet recording apparatus, noise in printing is relatively small and in addition, small dots can be formed in high density, such an ink jet recording apparatus is currently used for many types of printing including color printing.
The ink jet recording apparatus described above provided with an ink jet recording head to which ink from an ink cartridge is supplied, and a paper feeding mechanism for relatively moving recording paper under the recording head. The recording is performed by jetting ink droplets onto the recording paper, moving the recording head on a carriage in the widthwise direction of the recording paper.
Recording heads for jetting black ink and each color ink of yellow, cyan and magenta are mounted on the carriage, and full color printing is enabled by changing the ratio of the jetting of each ink in addition to text printing by black ink.
The above ink jet recording head has a problem that printing failure is caused by the increase of ink viscosity caused by the vaporization of a solvent from nozzle orifices, the solidification of ink, the adhesion of dust, further the mixture of bubbles or the like, because the printing is performed by jetting ink pressurized in the pressure generating chambers onto recording paper from nozzle orifices as an ink droplet.
Therefore, the above ink jet recording apparatus is provided with: a capping member normally composed of a plastic cap holder (cap case) and a cap made of elastic material such as rubber for sealing the nozzle orifices of the recording head while the printing is halted; and a cleaning member for cleaning a nozzle plate if necessary.
The above capping member not only functions as a cap for preventing ink at nozzle orifices from drying while printing is halted but is provided with functions for sealing the nozzle plate by the cap in case the nozzle orifices are clogged, sucking ink from the nozzle orifices by negative pressure generated by a suction pump as a negative pressure generating member, and solving the clogging caused by the solidification of ink at the nozzle orifices and a failure in the jetting of ink caused by bubbles mixed in an ink passage.
FIG. 23 schematically shows a state in which the nozzle-formed surface of the recording head is sealed by the capping member.
As shown in FIG. 23, the capping member 10 is provided with a rectangular cap case 10a the upper face of which is opened and a cap 10b housed in the cap case 10a and made of flexible material such as rubber material, and the cap 10b is formed so that the upper edge thereof is slightly protruded from the top face of the cap case 10a. 
An ink absorber 10c made of porous material is housed at the inner bottom of the cap 10b and is held by a holder 10d integrally formed with the cap 10b. 
A suction hole 10e and an air hole 10f are formed at the bottom of the cap case 10a and penetrate the cap case 10a and the cap 10b. 
A suction pump 11 as a negative pressure generating member is connected to the suction hole 10e of the cap case 10a via a tube T1 and discharge side of the suction pump 11 is connected to a waste ink tank 13.
Further, an air valve 14 is connected to the air hole 10f of the cap case 10a via a tube T2.
In the meantime, a reference number 7 in FIG. 23 denotes a recording head. As the capping member 10 is moved upwards when the recording head 7 is moved toward above the capping member 10, the nozzle-formed surface, that is, a nozzle plate 7a is sealed (capped) by the above cap 10b. 
Plural nozzle orifices 7b are formed on the nozzle plate 7a, and black ink and each color ink such as yellow, cyan and magenta are jetted by the action of a piezoelectric vibrator 7c arranged corresponding to each nozzle orifices 7b. 
Owing to the above structure, ink is sucked from the recording head in a state in which the cap 10b is adhesively contacted to the nozzle plate 7a of the recording head 7 and the air valve 14 is closed as shown in FIG. 23.
That is, negative pressure is applied to the internal space of the cap 10b by operating the suction pump 11 in this state and ink is discharged from the nozzle orifices 7b. 
When the above air valve 14 is opened while the suction pump is halted in a predetermined time and the negative pressure inside the cap decreases to some extent because ink is discharged, the air is introduced inside the cap and inside negative pressure is released.
When the suction pump 11 is operated again in a state in which the air valve 14 is opened, operation for sending ink discharged inside the cap to a waste ink tank 13 via the tube T1 is executed.
In the meantime, while the printing is halted, the nozzle-formed surface of the recording head, that is, the nozzle plate 7a is sealed by the cap 10b as shown in FIG. 23, the above air valve 14 is closed and the internal space of the cap 10b is kept moist by an ink solvent. Hereby, the nozzle orifices of the recording head is prevented from being clogged by drying, and the reliability of printing operation when printing is restarted can be secured.
However, there is a problem that the ink solvent is vaporized in a passage communicating from the internal space of the cap to the suction hole or the air hole and further, in a path which leads to the suction pump connected to the suction hole and the air hole and the air valve.
FIG. 24 shows an example which is a sectional view showing a passage making the internal space of a cap and a suction hole communicate in an example of a cap case in capping member currently used.
The same reference number is allocated to a part shown in FIG. 24 equivalent to the part already described and shown in FIG. 23 and therefore, the description is omitted.
As shown in FIG. 24, the passage 10g for making the internal space of the cap and the suction hole 10e communicate is formed so that the inner diameter is relatively large and the length is relatively short. A reference number 10n denotes a fitting member for fitting the cap.
As described above, in a state in which the passage 10g is formed so that the inner diameter is large and the length is short, there is a problem that flow resistance on the side of a suction pump is small and therefore, the vaporization to the outside of an ink solvent is caused in a tube connected to the suction pump.
Particularly, for the suction pump, a low-cost tube pump which is securely operated is used and for a tube composing the tube pump, elastic and restorable silicon rubber is used.
However, silicon rubber has a problem that it is relatively inferior in gas-barrier characteristic, and thereby an ink solvent would be vaporized from the tube to the outside.
Therefore, as an ink solvent is gradually vaporized from the internal space of the cap via the above passage and a moist state in the cap is deteriorated in case a recording apparatus is halted for a long term, clogging in the nozzle orifices of the recording head is caused.
After the recording apparatus is halted for a long term, so-called timer cleaning that ink is automatically sucked from the nozzle orifices of the recording head when the recording apparatus is powered on is executed, however, when the solid material of ink is deposited in the minute nozzle orifices of the recording head, it is not easy to remove the solid material by the suction of ink and a problem that the reliability of printing operation is deteriorated is caused.
The tube pump used for this type of recording apparatus is driven by utilizing the power of a paper feeding motor or the like which is not used while the printing is halted in order to suck ink from the nozzle orifices.
The above tube pump is composed of an arcuate face for supporting a tube therealong and a roller which rolls while pressing the tube onto the supporting face. Therefore, for the material of the tube composing the tube pump, elastic and restorable silicon rubber is generally used.
The sucking side of the tube made of silicon rubber is connected to the suction hole of the above capping member.
If the above silicon rubber is used for the tube pump, the elastic and restorable characteristic can be utilized, however, silicon rubber has a problem that it is relatively inferior in the gas-barrier characteristic as described in the above, a rate in which an ink solvent is vaporized from the tube to the outside is considerably large.
Further, recently, as a cap is also lengthened according to the large sizing of a recording head, there is a problem that deflection and deformation are easily caused when the cap is touched to the recording head, a gap is made between the recording head and the cap and airtightness is deteriorated.
Such a problem can be solved by forming pleats at the top end of the cap in order to balance rigidity and elasticity, and suitably installing the cap in a cap holder. However, there is a problem that initial performance cannot be fulfilled by the aging change of the rigidity and elasticity of the cap, the reliability is deteriorated and others in addition to a problem that the process becomes complicated.
To solve such problems, as disclosed in Japanese Patent Publication Nos. 61-213145A and 8-99331A for example, it is proposed that a member to function as a base is formed by first polymeric material by injection molding and an attachment is fixed by using the metallic mold as it is or reinstalling the base in a second metallic mold and injection-molding second polymeric material on the base.
However, it is very difficult to acquire sufficient precision to form a packing member the volume of which is at most substantially 20 cc and the thickness of which is a few mm as a cap for sealing nozzle orifices.
The present invention is made to solve the problems of the above related ink jet recording apparatus and the object is to provide an ink jet recording apparatus wherein a moist state in the internal space of a capping member can be maintained for a long term and the reliability of printing by a recording head can be enhanced.
Another object of the present invention is to provide a capping unit by which the recording head can be securely sealed for a long term and a method of manufacturing the same simply.
In order to achieve the above objects, there is provided an ink jet recording apparatus comprising: an ink jet recording head having a surface provided with nozzle orifices from which ink droplets are ejected; and a capping member for sealing the surface provided with the nozzle orifices to apply negative pressure generated by a negative pressure generating member. The capping member includes: a cap made of flexible material, which is to be abutted against the surface provided with the nozzle orifices; a cap case for holding the cap; a suction hole to which the negative pressure generating member is connected; and a first passage formed in either the cap or the cap case for communicating the internal space with the suction hole.
In the apparatus, the capping member may further include: an air hole to which a valve introducing external air into an internal space defined by the cap; and a second passage formed in either the cap and the cap case for communicating the internal space with the air hole. Here, at least the first passage between the first and second passages is formed into a shape capable of inhibiting vaporization of an ink solvent in the internal space.
In the apparatus, the cap may be bonded on an inner face of the cap case.
In the apparatus, the cap may be integrally formed on an upper portion of the cap case.
In the apparatus, a cylindrical body may be formed integrally with the cap case so as to protruded from a bottom face of the case. At least the first passage between the first and second passages may be formed in the cylindrical body.
In the apparatus, a metal tube member may be inserted into at least the suction hole between the suction hole and the air hole.
In the apparatus, at least the first passage between the first and second passages may be formed by a groove formed along an outer peripheral face of the cap case and a seal member for sealing the groove. The sealing member may be made of at least one material selected from the group consisting of an aluminum deposited film, a silicon oxide deposited film, polyethylene terephthalate, undrawn polypropylene, ethylene-vinylalcohol, ethylene-vinyl acetate copolymer, polyvinylidene chloride, and cyclic olefin copolymer.
In the apparatus, at least the first passage between the first and second passages may be formed by a groove formed on the inner face of the cap case.
In the apparatus, at least the first passage between the first and second passages may be formed by a groove formed on a bottom face of the cap.
According to the ink jet recording apparatus configured as described above, the vaporization of the ink solvent from the internal space is inhibited. Hereby, a moist state of an ink solvent in the internal space of the capping member can be maintained for a long term.
Therefore, the degree of the occurrence of the clogging of nozzle orifices in the recording head while the recording apparatus is halted for a long term can be reduced, a frequency in which so-called timer cleaning is executed can be reduced and if timer cleaning is executed, the reliability of printing in the recording head can be sufficiently recovered.
The apparatus further comprises: a first tube made of a material having high gas-barrier characteristic and connected to the suction hole; and a second tube member made of an elastic and restorative material for connecting the negative pressure generating member with the first tube.
In the apparatus, the negative pressure generating member is a tube pump including a supporting face for supporting the second tube in the shape of an arc and a roller rotating while pressing the second tube onto the supporting face.
In the apparatus, a tube made of butyl rubber is used as the first tube, and a tube made of silicon rubber is used as the second tube.
According to the ink jet recording apparatus configured as described above, the vaporization of an ink solvent from the tube while the recording apparatus is halted can be effectively inhibited.
Therefore, the degree of the occurrence of the clogging of nozzle orifices in the recording head while the recording apparatus is halted for a long term can be reduced and the reliability of printing in the recording head can be sufficiently recovered by executing so-called timer cleaning.
If the recording apparatus is halted for relatively a short term, the reliability of printing can be secured without executing the above timer cleaning.
In the apparatus, the cup casing may be formed into a shape of cup having a brim portion on which an annular groove into which the cap is fitted is formed.
In the apparatus, the cap case may be made of polymeric material, and the cap may be made by the injection molding of the flexible material.
In the apparatus, the width of a bottom face of the cap may be equal or wider than the width of the brim portion of the cap casing.
In the apparatus, the cap may be bonded onto the brim portion of the cap case.
In the apparatus, the cap case may be made of either polypropylene or polyethylene, and the cap may be made of either styrene thermoplastic elastomer or styrene thermoplastic elastomer composite materials.
In the apparatus, the groove may be provided with a portion communicating with the outside.
In the apparatus, the injection molding is conducted by the steps of: sealing the groove on the brim portion by a mold defining a shape of the cap; and injecting the material which is to be the cap into the mold.
In the apparatus, a first port from which the material which is to be the cap is injected and a second port from which air in the mold is discharged is formed in either the groove on the brim portion or the mold.
According to the ink jet recording apparatus configured as described above, the cap case having high rigidity can be prevented from being deformed, and the whole periphery of the cap held by the cap case can be uniformly deformed owing to elasticity controlled depending upon the height thereof. Therefore, the airtightness of the cap for the recording head can be secured.